I. Field of the Invention
The Present invention relates generally to a method and system for reducing engine knock in an internal combustion engine.
II. Description of the Prior Art
High engine load and overheated engine cylinders are the primary causes of engine knock in internal combustion engines. When knock occurs in an internal combustion engine, vibrations composed of specific resonant frequencies occur. With reference to FIG. 1, the vibration spectrum produced by various types of engine knock is thereshown. The simplest type of engine knock is usually caused by a single self combustion resulting from an overheated combustion chamber. Such a condition causes a monotonous or single knock and thus produces a vibration peak at approximately 6 kHz as indicated by arrow 10.
The other resonant vibration modes are caused by more complex knock phenomena. One such complex knock phenomena occurs from simultaneous combustion at different cylinder portions beside the cylinder wall. This complex knock phenomena usually results from high engine loads and results in higher resonant vibration frequencies illustrated by the peaks 12-15 in FIG. 1.
Consequently, overheated combustion chambers create resonant frequency vibrations at a relatively low frequency while high engine load conditions result in engine knock at higher resonant vibration frequencies.
With reference then to FIG. 2, a graph 16 is thereshown illustrating the relation between combustion cylinder temperature and the combustion cylinder pressure for a typical internal combustion engine In the region 18 below the graph, normal or no knock operation of the engine occurs. Conversely, in the region 20 above the graph 16, engine knock occurs.
Still referring to FIG. 2, engine knock caused by a single self combustion resulting from an overheated combustion chamber will produce engine operation in the area indicated at arrow 22. The correction of such knock is most efficiently corrected by increasing the fuel flow to the engine cylinder thus reducing the temperature of the engine cylinder and moving the engine operation into the normal, no knock region 18 as indicated at arrow 23.
Conversely, multiple simultaneous knocks caused by high engine load will create a knocking condition in the region indicated by arrow 24. Such a knock is most efficiently corrected by retarding the spark ignition and moving the engine operation into the normal operation region 18 as shown by arrow 25.
Lastly, an engine operating condition having both single knocks and multiple cylinder knocks will create an engine operation in the area indicated by arrow 26. In such a situation, both an increase of the fuel supply to the engine, as well as retardation of the spark ignition is the most efficient way to reduce the engine knock and to restore engine operation into the normal operation region 18 as shown by arrow 27.
There have been previously known engine knock detectors and which vary the fuel supply and/or the spark ignition timing as a function of the engine vibration. These previously known engine knock detectors, however, only measure a single, fixed resonant frequency spectrum by utilizing a band pass filter. Consequently, these previously known knock detectors are incapable of differentiating between single knocks caused by overheated combustion chamber and multiple knocks caused by high load engine operation. Similarly, since these previously known systems utilize band pass filters to detect engine knock only within a relatively narrow frequency spectrum, engine vibration resulting from engine knock outside the band pass frequency spectrum remains undetected and, therefore, uncorrected.
For all of the foregoing reasons, the previously known engine knock detection systems are relatively inefficient and inadequate.